Method and apparatus for reducing impact force in a ball-seat assembly

ABSTRACT

A method of restricting fluid flow includes: releasing a ball into a fluid conduit and receiving the ball in a ball receiving element disposed at the fluid conduit and at least partially restricting fluid flow; and at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element by a reflective boundary disposed in the fluid conduit.

BACKGROUND

In the drilling and completion industry and for example in hydrocarbonexploration and recovery operations, a variety of components and toolsare lowered into a borehole for various operations such as productionoperations, for example. Some downhole tools utilize ball-seatassemblies to act as a valve or actuator. Ball-seat assemblies are usedwith, for example, hydraulic disconnects, circulating subs andinflatable packers.

Actuation of a ball-seat assembly generally includes releasing a ball orother plug from a releasing mechanism and allowing the ball to drop ontothe ball seat and restrict a fluid conduit. The impact between the balland the ball seat can produce pressure waves, which can cause wearand/or damage to the ball-seat assembly and other components. Forexample, initial impact is generally the most severe and is compoundedby the suction pressure on the ball seat due to an outgoing expansionwave downstream of the seating area.

SUMMARY

A method of restricting fluid flow includes: releasing a ball into afluid conduit and receiving the ball in a ball receiving elementdisposed at the fluid conduit and at least partially restricting fluidflow; and at least partially reflecting one or more pressure wavesresulting from an impact between the ball and the ball receiving elementby a reflective boundary disposed in the fluid conduit.

An apparatus for restricting fluid flow includes: a ball receivingelement disposed in a fluid conduit and configured to receive a ballthat has been advanced through the fluid conduit and at least partiallyrestrict fluid flow; and a reflective boundary disposed in the fluidconduit at least partially reflecting one or more pressure wavesresulting from an impact between the ball and the ball receivingelement.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a cross-sectional view of a subterranean well drilling, welllogging, evaluation, exploration and/or production system

FIG. 2 is a flow diagram depicting a method of restricting fluid flow ina conduit;

FIG. 3 is a cross-sectional view of an embodiment of a ball-seatassembly including a first and a second fluid injected into a conduit ofthe ball-seat assembly; and

FIG. 4 is a cross-sectional view of an embodiment of a ball-seatassembly including a first and second fluid injected into a conduit ofthe ball-seat assembly.

DETAILED DESCRIPTION

The apparatuses, systems and methods described herein provide forcontrolling downhole fluid flow and mitigating pressure waves caused byactuation of a ball-seat assembly. A downhole actuator assembly includesa conduit having a longitudinal component to guide a ball released intothe conduit to a ball receiving element such as a ball seat. Areflective boundary disposed in the conduit at least partially reflectsone or more pressure waves resulting from an impact between the ball andthe ball receiving element. One embodiment of a method of reducingpressure waves includes pumping a first downhole fluid into the conduit,followed by pumping a second downhole fluid that has a characteristicthat is different than the characteristic of the first downhole fluid,which creates a reflective boundary from the interface between the firstand second fluids that acts to reflect incident pressure waves createdby an impact between the ball and the ball receiving element. Thereflected pressure waves destructively interfere with the incidentpressure waves to reduce the amplitude of the incident pressure wavesand reduce wear on downhole components such as the ball and the ballseat. Examples of such characteristics include density, viscosity,polarity, and chemical and/or physical differences causing the fluids toresist mixing or combining.

Referring to FIG. 1, an exemplary embodiment of a subterranean welldrilling, well logging, evaluation, exploration and/or production system10 includes a borehole string 12 such as a production string that isshown disposed in a borehole 14 that penetrates at least one earthformation 16 during a subterranean operation. The borehole string mayinclude any type of carrier, such as a downhole sub or wireline. A tool18, such as a ball seat sub, includes a housing 20 having a longitudinalbore or fluid conduit 22. A ball-seat assembly includes a ball receivingelement such as a ball seat 24 included in the conduit 22 to retain aball 26 that is released into the conduit 14. In one embodiment, theball 26 is a spherical metal or plastic plug, although “ball” may referto any type of moveable or droppable plugging element, such as a dropplug, and may take any desired shape or size. Actuation of the ball seatassembly includes releasing the ball into the fluid conduit 14, forexample by dropping the ball 18 into and/or pumping the ball 18 throughthe fluid conduit 14 from a surface or downhole location. The ball 18falls and/or is advanced by downhole fluid toward the ball seat 16 andis seated on the ball seat 16 to restrict fluid flow through the conduit14.

The ball seat 24 may be an annular component connected to the conduit22, or any other device or configuration providing a restriction in thediameter or cross-sectional area of the conduit 22 sufficient to preventthe ball 26 from passing therethrough. For example, the ball seat 24 maybe attached to the inner surface of the conduit 22 or include a reduceddiameter portion of the conduit 22.

In one embodiment, the tool 18 is configured to be in fluidcommunication with at least one pumping device 28 that is configured tointroduce into and/or advance a fluid through the borehole string 12 andthe fluid conduit 22. In one embodiment, a processor or other device,such as a surface processing unit 30 is in operable communication withthe pumping device 28 and/or the tool 18 to communicate with and controloperation of the pumping device 28 and/or the ball-seat assembly. Thedownhole tool 10 is not limited to that described herein. The boreholestring 12 and/or the tool 18 may include any tool, carrier or componentthat includes a ball seat assembly. In addition, the tool 18 is notlimited to components configured for downhole use.

FIG. 2 illustrates a method 40 of restricting fluid flow in a component.The method includes, for example, actuating a valve or packer in adownhole assembly. The method 40 includes one or more stages 41-43.Although the method is described in conjunction with the system 10 andthe downhole tool 18, the method can be utilized in conjunction with anydevice or system (configured for downhole or surface use) that utilizesa ball-seat assembly.

In the first stage 41, in one embodiment, the downhole tool 18 isdeployed downhole and advanced along the borehole 14 to a desiredposition, such as via a borehole string 12 or a wireline. In the secondstage 42, a first downhole fluid having a first characteristic such as afirst density is injected, pumped or otherwise introduced into the fluidconduit 22. In the third stage 43, a second downhole fluid having asecond characteristic such as a second density is introduced into thefluid conduit 22 at a time proximate to or otherwise dependent on a timeof release of the ball 18 or an anticipated time of actuation of theball-seat assembly. In the fourth stage 44, the ball-seat assembly isactuated by releasing the ball 26 into the conduit 22, for example bydropping the ball 18 into the conduit 14 and/or pumping the ball 18through the conduit 14. The ball 18 advances through the conduit 14 andimpacts the ball seat 16. The different characteristics of the first andsecond downhole fluids create an interface or boundary that acts toreflect one or more incident pressure waves resulting from an impactbetween the ball 26 and the ball seat 24. The pressure wavesdestructively interfere with the incident pressure waves and dissipatethe pressure waves to reduce the severity and duration of loads createdby the pressure waves. This dissipation may also reduce the suctionpressure on the ball-seat assembly due to the outgoing expansion wavedownstream of the seating area. The different characteristics may be anycharacteristics sufficient to create a reflective boundary between thefirst and second fluids. For example, the fluids may have differentdensities or viscosities. In one embodiment, the fluids may havedifferent chemical polarities. For example, the first fluid may be agenerally polar fluid such as a water-based fluid and the second fluidmay be a generally non-polar fluid such as an oil-based fluid.

An embodiment of the method 40 is described in conjunction with FIG. 3,which shows an embodiment of a ball-seat assembly 50. In thisembodiment, a first downhole fluid 52 is pumped into the fluid conduit22 via, for example, the borehole string 12. The ball 26 is releasedupon actuation of the ball-seat assembly 50, and at a selected timeafter ball release, a second downhole fluid 54 is pumped into theconduit 22. The first fluid 52 pumped ahead of the ball 26 has a firstdensity ‘A’ that is different than a second density ‘B’ of the secondfluid 54 pumped right after the ball. In one embodiment, the density Ais greater than the density B, although the density A may be less thanthe density B in other embodiments. Various types of fluids may be used,such as water having a density of 8.3 pounds per gallon (ppg) andvarious drilling muds, such as water based drilling fluids havingvarious densities (e.g., 16.5 ppg), and oil based muds which may havevarious densities ranging from, for example, 8-18 ppg.

The interface between fluids having the densities A and B results in aboundary 56 that provides a surface for the reflection of the incidentpressure wave(s). Reflected pressure waves reflected from the boundary56 at least partially cancel out the original pressure wave(s) createdat the time of impact and reduces the net pressure resulting fromimpact.

The pumping of the second fluid 54 is initiated at a time so that theboundary 56 advances with the ball 26 at a selected distance from theball 26. In this way, the distance of the boundary 56 from the ball 26and the ball seat 24 at the time of impact can be controlled. Forexample, the injection or pumping of the second fluid 54 is triggeredprior to or in anticipation of ball-seat actuation so that the boundary56 is formed upstream and/or downstream of the ball 26. The pumping ofthe second fluid 54 may be initiated so that the boundary 56 isproximate to the ball 26, so that the boundary 56 is located proximateto the ball seat 24 at time of impact to rapidly dissipate the incidentpressure wave(s).

Another embodiment of the method 40 is described in conjunction withFIG. 4. In this embodiment, the first fluid 52 of density ‘A’ is pumpedfirst, followed by the second fluid 54 of density ‘B’ which carries theball. Density B may be, for example, greater than density A. In oneembodiment, the second fluid 54 is injected at a time relative toball-seat assembly actuation so that the ball 26 is carried by thesecond fluid and the boundary 56 is downhole of the ball 26 but stillclose to the ball 26. Upon impact, the boundary 56 is downhole of theball 26 and the incident pressure wave is a negative expansion waveformbut the dense fluid reflection is a positive or compression wave thatwill tend to cancel the tensile or negative wave. Thus the amount offorce on the ball 26 will be less because the pulling force from belowwill be cancelled out by the reflected waves. In one embodiment, thefirst fluid 52 of density ‘A’ (or another fluid having a densitydifferent than the density ‘B’) is additionally injected or pumpedfollowing the second fluid 54. The density difference between A and Bthus creates a density contrast, i.e., a boundary 56, relative to theball at both upstream and downstream locations. Impact of the ball 26upon the ball seat 24 creates a pressure wave in both the upstream anddownstream directions, which are at least partially reflected anddissipated by the boundaries 56. Thus the net pressure on the ball-seatassembly 50 resulting from the impact is reduced by successively pumpingdifferent density fluids.

The apparatuses and methods described herein provide various advantagesover existing processing methods and devices. Wear on the ball-seatassembly, which is a function of force over distance and time, can bereduced by reducing the force of the ball of the seat through thereduction in amplitude of the pressure wave(s). This reduction directlyreduces the probability of ball-seat damage and conversely improves itsreliability. The reduction of pressure waves affecting the ball-seatassembly can enable the use of a wider range of construction materialsand reduce the cost and complexity of ball-seat design, for example byreducing the need for relatively complex ball seat designs to reduceimpact. In addition, the apparatuses and methods can allow for the ballseat to have a larger inner diameter due to the reduced contact stress.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications will be appreciated by those skilled in theart to adapt a particular instrument, situation or material to theteachings of the invention without departing from the essential scopethereof. Therefore, it is intended that the invention not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this invention.

1. A method of restricting fluid flow, comprising: releasing a ball intoa fluid conduit and receiving the ball in a ball receiving elementdisposed at the fluid conduit and at least partially restricting fluidflow; and at least partially reflecting one or more pressure wavesresulting from an impact between the ball and the ball receiving elementby a reflective boundary disposed in the fluid conduit.
 2. The method ofclaim 1, wherein the fluid conduit includes a first fluid having a firstcharacteristic.
 3. The method of claim 2, further comprising injecting asecond fluid into the fluid conduit, the second fluid having a secondcharacteristic different than the first characteristic and configured toform an interface between the first fluid and the second fluid, theinterface forming the reflective boundary.
 4. The method of claim 3,wherein the characteristic is selected from at least one of a polarity,a viscosity, a chemical composition and a physical composition.
 5. Themethod of claim 3, wherein the first characteristic is a first densityand the second characteristic is a second density.
 6. The method ofclaim 1, wherein at least partially reflecting includes generating atleast one reflected wave that destructively interferes with the one ormore pressure waves.
 7. The method of claim 3, wherein the second fluidis injected at a time that is dependent on a release time of the ball sothat the interface is located at a selected distance relative to theball at impact.
 8. The method of claim 3, wherein the second fluid isinjected at a time that is dependent on a release time of the ball sothat the interface is located at least one of upstream and downstream ofthe ball receiving element at impact.
 9. The method of claim 7, furthercomprising injecting an additional fluid after the second fluid, theadditional fluid having a characteristic different than the secondcharacteristic so that the interface is located both upstream anddownstream of the ball receiving element at impact.
 10. The method ofclaim 1, further comprising disposing a carrier including the actuatorassembly in a borehole.
 11. An apparatus for restricting fluid flow,comprising: a ball receiving element disposed in a fluid conduit andconfigured to receive a ball that has been advanced through the fluidconduit and at least partially restrict fluid flow; and a reflectiveboundary disposed in the fluid conduit at least partially reflecting oneor more pressure waves resulting from an impact between the ball and theball receiving element.
 12. The apparatus of claim 11, wherein theboundary at least partially reflects one or more pressure wavesresulting from an impact between the ball and the ball receivingelement, and generates at least one reflected pressure wave thatdestructively interferes with the one or more pressure waves.
 13. Theapparatus of claim 11, wherein the fluid conduit is configured toreceive a first fluid having a first characteristic.
 14. The apparatusof claim 13, wherein the fluid conduit is configured to receive a secondfluid, the second fluid having a second characteristic different thanthe first characteristic and configured to form an interface between thefirst fluid and the second fluid, the interface forming the reflectiveboundary.
 15. The apparatus of claim 14, wherein the characteristic isselected from at least one of a polarity, a viscosity, a chemicalcomposition and a physical composition.
 16. The apparatus of claim 14,wherein the first characteristic is a first density and the secondcharacteristic is a second density.
 17. The apparatus of claim 14,further comprising a processor configured to inject the second fluid ata time that is dependent on a release time of the ball so that theinterface is located at a selected distance relative to the ball atimpact.
 18. The apparatus of claim 14, further comprising a processorconfigured to inject the second fluid at a time that is dependent on arelease time of the ball so that the interface is located at least oneof upstream and downstream of the ball receiving element at impact. 19.The apparatus of claim 18, wherein the processor is configured to injectan additional fluid after the second fluid, the additional fluid havinga characteristic different than the second characteristic so that theinterface is located both upstream and downstream of the ball receivingelement at impact.
 20. The apparatus of claim 11, further comprising acarrier including the ball receiving element and the fluid conduit, thecarrier configured to be disposed in a borehole.